//! 现代异步I/O框架实现

use std::future::Future;
use std::pin::Pin;
use std::collections::HashMap;
use std::fs::{File, OpenOptions};
use std::io::{Read, Seek, SeekFrom, Write};
use std::sync::{Arc, Mutex, RwLock, atomic::AtomicU64, atomic::Ordering};
use std::time::Instant;
use tokio::runtime::Runtime;
use tokio::sync::{mpsc, Semaphore};
use tokio::sync::mpsc::{Receiver};
use tokio::sync::mpsc::error::TryRecvError;
use std::task::{Context, Poll, Waker};
use std::path::Path;
use tokio::runtime::Builder;
use tokio::task::{JoinHandle, spawn_blocking};
use tokio::time::Duration;

use crate::core::error::{FFIError, FFIResult};
use crate::core::memory::SafeMemoryBuffer;

/// 异步I/O操作类型
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum AsyncIOType {
    /// 读取操作
    Read,
    /// 写入操作
    Write,
    /// 寻求操作
    Seek,
    /// 内存映射操作
    MemoryMap,
}

/// 异步I/O请求
struct AsyncIORequest {
    /// 操作类型
    op_type: AsyncIOType,
    /// 文件路径
    file_path: String,
    /// 缓冲区
    buffer: Option<Arc<Mutex<SafeMemoryBuffer>>>,
    /// 偏移量
    offset: u64,
    /// 长度
    length: usize,
    /// 寻求位置
    seek_position: Option<SeekFrom>,
    /// 完成回调
    completion_callback: Option<Box<dyn FnOnce(FFIResult<usize>) + Send + Sync>>,
    /// 操作ID
    op_id: u64,
    /// 请求优先级
    priority: u8,
}

impl Clone for AsyncIORequest {
    fn clone(&self) -> Self {
        AsyncIORequest {
            op_type: self.op_type,
            file_path: self.file_path.clone(),
            buffer: self.buffer.clone(),
            offset: self.offset,
            length: self.length,
            seek_position: self.seek_position,
            completion_callback: None, // 克隆时移除回调函数
            op_id: self.op_id,
            priority: self.priority,
        }
    }
}

impl AsyncIORequest {
    /// 创建新的异步I/O请求
    fn new(
        op_type: AsyncIOType,
        file_path: &str,
        buffer: Option<Arc<Mutex<SafeMemoryBuffer>>>,
        offset: u64,
        length: usize,
        seek_position: Option<SeekFrom>,
        completion_callback: Option<Box<dyn FnOnce(FFIResult<usize>) + Send + Sync>>,
        op_id: u64,
        priority: u8
    ) -> Self {
        AsyncIORequest {
            op_type,
            file_path: file_path.to_string(),
            buffer,
            offset,
            length,
            seek_position,
            completion_callback,
            op_id,
            priority,
        }
    }
}

/// 异步I/O任务状态
enum AsyncIOTaskState {
    /// 等待中
    Pending,
    /// 进行中
    Running,
    /// 已完成
    Completed(FFIResult<usize>),
    /// 已取消
    Cancelled,
}

/// 异步I/O任务
struct AsyncIOTask {
    /// 任务状态
    state: Arc<RwLock<AsyncIOTaskState>>,
    /// 任务句柄
    handle: Option<JoinHandle<()>>,
    /// 操作ID
    op_id: u64,
    /// Waker
    waker: Arc<RwLock<Option<Waker>>>,
}

impl AsyncIOTask {
    /// 创建新的异步I/O任务
    fn new(op_id: u64) -> Self {
        AsyncIOTask {
            state: Arc::new(RwLock::new(AsyncIOTaskState::Pending)),
            handle: None,
            op_id,
            waker: Arc::new(RwLock::new(None)),
        }
    }
    
    /// 设置任务状态
    fn set_state(&self, state: AsyncIOTaskState) {
        if let Ok(mut state_guard) = self.state.write() {
            *state_guard = state;
        }
        
        // 唤醒等待的任务
        if let Ok(waker_guard) = self.waker.read() {
            if let Some(waker) = waker_guard.clone() {
                waker.wake();
            }
        }
    }
}

/// 异步I/O操作未来
pub struct AsyncIOFuture {
    /// 任务引用
    task: Arc<AsyncIOTask>,
}

impl Future for AsyncIOFuture {
    type Output = FFIResult<usize>;
    
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let state = self.task.state.read().unwrap();
        
        match &*state {
            AsyncIOTaskState::Pending => {
                // 保存waker并更新状态为Running
                if let Ok(mut state_guard) = self.task.state.write() {
                    *state_guard = AsyncIOTaskState::Running;
                }
                if let Ok(mut waker_guard) = self.task.waker.write() {
                    *waker_guard = Some(cx.waker().clone());
                }
                Poll::Pending
            },
            AsyncIOTaskState::Running => {
                // 更新waker
                if let Ok(mut waker_guard) = self.task.waker.write() {
                    *waker_guard = Some(cx.waker().clone());
                }
                Poll::Pending
            },
            AsyncIOTaskState::Completed(result) => {
                // 返回完成的结果
                Poll::Ready(result.clone())
            },
            AsyncIOTaskState::Cancelled => {
                // 返回取消错误
                Poll::Ready(Err(FFIError::Cancelled("Operation cancelled".to_string())))
            },
        }
    }
}

/// 异步I/O调度器
pub struct AsyncIOScheduler {
    /// 运行时
    runtime: Arc<Mutex<Option<Runtime>>>,
    /// 请求通道发送器
    request_sender: Option<mpsc::Sender<AsyncIORequest>>,
    /// 请求通道接收器
    request_receiver: Option<Arc<Mutex<mpsc::Receiver<AsyncIORequest>>>>,
    /// 最大并发任务数
    max_concurrent_tasks: u32,
    /// 信号量
    semaphore: Arc<Semaphore>,
    /// 任务映射
    tasks: Arc<RwLock<HashMap<u64, Arc<AsyncIOTask>>>>,
    /// 下一个操作ID
    next_op_id: AtomicU64,
    /// 线程池大小
    thread_pool_size: usize,
}

impl AsyncIOScheduler {
    /// 创建新的异步I/O调度器
    pub fn new(max_concurrent_tasks: u32, thread_pool_size: usize) -> Self {
        // 创建请求通道
        let (sender, receiver) = mpsc::channel(1000);
        
        AsyncIOScheduler {
            runtime: Arc::new(Mutex::new(None)),
            request_sender: Some(sender),
            request_receiver: Some(Arc::new(Mutex::new(receiver))),
            max_concurrent_tasks,
            semaphore: Arc::new(Semaphore::new(max_concurrent_tasks as usize)),
            tasks: Arc::new(RwLock::new(HashMap::new())),
            next_op_id: AtomicU64::new(1),
            thread_pool_size,
        }
    }
    
    /// 初始化调度器
    pub fn initialize(&mut self) -> FFIResult<()> {
        // 创建运行时
        let runtime = Builder::new_multi_thread()
            .worker_threads(self.thread_pool_size)
            .thread_name("async-io-worker")
            .enable_all()
            .build()
            .map_err(|e| FFIError::InitializationFailed(format!("Failed to create runtime: {}", e)))?;
        
        // 存储运行时
        if let Ok(mut runtime_guard) = self.runtime.lock() {
            *runtime_guard = Some(runtime);
        }
        
        // 启动请求处理器
        self.start_request_processor()?;
        
        log::info!("Async I/O scheduler initialized with {} concurrent tasks and {} threads", 
                  self.max_concurrent_tasks, self.thread_pool_size);
        
        Ok(())
    }
    
    /// 启动请求处理器
    fn start_request_processor(&self) -> FFIResult<()> {
        if let Ok(runtime_guard) = self.runtime.lock() {
            if let Some(runtime) = &*runtime_guard {
                let receiver = self.request_receiver.clone().unwrap();
                let semaphore = self.semaphore.clone();
                let tasks = self.tasks.clone();
                
                // 在运行时中启动请求处理器
                runtime.spawn(async move {
                    Self::process_requests(receiver, semaphore, tasks).await;
                });
                
                return Ok(());
            }
        }
        
        Err(FFIError::InitializationFailed("Runtime not initialized".to_string()))
    }
    
    /// 处理请求
    async fn process_requests(
        receiver: Arc<Mutex<mpsc::Receiver<AsyncIORequest>>>,
        semaphore: Arc<Semaphore>,
        tasks: Arc<RwLock<HashMap<u64, Arc<AsyncIOTask>>>>
    ) {
        loop {
            // 尝试获取请求，但确保锁不会跨越await点
            let request = match receiver.lock() {
                Ok(mut receiver_guard) => {
                    // 尝试非阻塞接收
                    match receiver_guard.try_recv() {
                        Ok(req) => Some(req),
                        Err(TryRecvError::Empty) => None, // 通道为空，稍后重试
                        Err(TryRecvError::Disconnected) => {
                            // 通道已关闭
                            break;
                        }
                    }
                },
                Err(_) => {
                    // 获取锁失败
                    None
                }
            };
            
            // 如果没有请求，等待一小段时间后重试
            let request = match request {
                Some(req) => req,
                None => {
                    tokio::time::sleep(Duration::from_millis(10)).await;
                    continue;
                }
            };
            
            // 现在我们有了请求，可以进行可变借用
            let mut request = request;
            
            // 获取信号量许可
            let _permit = match semaphore.acquire().await {
                Ok(permit) => permit,
                Err(_) => {
                    // 获取许可失败，调用完成回调（如果有）
                    if let Some(callback) = request.completion_callback.take() {
                        callback(Err(FFIError::Other("Too many concurrent operations".to_string())));
                    }
                    continue;
                },
            };
            
            // 查找对应的任务
            let task = if let Ok(tasks_guard) = tasks.read() {
                tasks_guard.get(&request.op_id).cloned()
            } else {
                None
            };
            
            // 处理请求
            let completion_callback = request.completion_callback.take();
            
            // 生成一个任务来处理I/O操作
            tokio::spawn(async move {
                let request_clone = request.clone();
                
                // 异步执行I/O操作
                let result = spawn_blocking(move || {
                    match request_clone.op_type {
                        AsyncIOType::Read => Self::execute_read(&request_clone),
                        AsyncIOType::Write => Self::execute_write(&request_clone),
                        AsyncIOType::Seek => Self::execute_seek(&request_clone),
                        AsyncIOType::MemoryMap => Self::execute_memory_map(&request_clone),
                    }
                }).await;
                
                // 处理结果
                let result = result.unwrap_or_else(|e| {
                    Err(FFIError::IOError(format!("Task execution failed: {}", e)))
                });
                
                // 更新任务状态
                if let Some(task) = &task {
                    task.set_state(AsyncIOTaskState::Completed(result.clone()));
                }
                
                // 调用完成回调（如果有）
                if let Some(callback) = completion_callback {
                    callback(result);
                }
            });
            
            // 信号量许可会在异步任务完成后自动释放
        }
    }
    
    /// 执行读取操作
    fn execute_read(request: &AsyncIORequest) -> FFIResult<usize> {
        // 打开文件
        let file = OpenOptions::new()
            .read(true)
            .open(&request.file_path)
            .map_err(|e| FFIError::IOError(format!("Failed to open file: {}", e)))?;
        
        // 创建文件句柄的可变引用
        let mut file = file;
        
        // 寻求到指定位置
        if request.offset > 0 {
            file.seek(SeekFrom::Start(request.offset))
                .map_err(|e| FFIError::IOError(format!("Seek failed: {}", e)))?;
        }
        
        // 读取数据到缓冲区
        if let Some(buffer) = &request.buffer {
            if let Ok(mut buffer_guard) = buffer.lock() {
                let buffer_slice = buffer_guard.as_mut_slice();
                let read_length = std::cmp::min(request.length, buffer_slice.len());
                
                let bytes_read = file.read(&mut buffer_slice[..read_length])
                    .map_err(|e| FFIError::IOError(format!("Read failed: {}", e)))?;
                
                Ok(bytes_read)
            } else {
                Err(FFIError::LockFailed("Failed to lock buffer".to_string()))
            }
        } else {
            Err(FFIError::InvalidArgument("No buffer provided for read operation".to_string()))
        }
    }
    
    /// 执行写入操作
    fn execute_write(request: &AsyncIORequest) -> FFIResult<usize> {
        // 打开文件（如果不存在则创建）
        let file = OpenOptions::new()
            .write(true)
            .create(true)
            .open(&request.file_path)
            .map_err(|e| FFIError::IOError(format!("Failed to open file: {}", e)))?;
        
        // 创建文件句柄的可变引用
        let mut file = file;
        
        // 寻求到指定位置
        if request.offset > 0 {
            file.seek(SeekFrom::Start(request.offset))
                .map_err(|e| FFIError::IOError(format!("Seek failed: {}", e)))?;
        }
        
        // 从缓冲区写入数据
        if let Some(buffer) = &request.buffer {
            if let Ok(buffer_guard) = buffer.lock() {
                let buffer_slice = buffer_guard.as_slice();
                let write_length = std::cmp::min(request.length, buffer_slice.len());
                
                let bytes_written = file.write(&buffer_slice[..write_length])
                    .map_err(|e| FFIError::IOError(format!("Write failed: {}", e)))?;
                
                // 刷新文件缓冲区
                file.flush()
                    .map_err(|e| FFIError::IOError(format!("Flush failed: {}", e)))?;
                
                Ok(bytes_written)
            } else {
                Err(FFIError::LockFailed("Failed to lock buffer".to_string()))
            }
        } else {
            Err(FFIError::InvalidArgument("No buffer provided for write operation".to_string()))
        }
    }
    
    /// 执行寻求操作
    fn execute_seek(request: &AsyncIORequest) -> FFIResult<usize> {
        // 打开文件
        let file = OpenOptions::new()
            .read(true)
            .write(true)
            .open(&request.file_path)
            .map_err(|e| FFIError::IOError(format!("Failed to open file: {}", e)))?;
        
        // 创建文件句柄的可变引用
        let mut file = file;
        
        // 执行寻求操作
        let position = if let Some(seek_pos) = &request.seek_position {
            file.seek(*seek_pos)
                .map_err(|e| FFIError::IOError(format!("Seek failed: {}", e)))?
        } else {
            file.seek(SeekFrom::Start(0))
                .map_err(|e| FFIError::IOError(format!("Seek failed: {}", e)))?
        };
        
        Ok(position as usize)
    }
    
    /// 执行内存映射操作
    fn execute_memory_map(_request: &AsyncIORequest) -> FFIResult<usize> {
        // 这里实现内存映射逻辑
        // 简化实现：返回请求的长度
        Ok(_request.length)
    }
    
    /// 异步读取文件
    pub fn async_read(
        &self,
        file_path: &str,
        buffer: Arc<Mutex<SafeMemoryBuffer>>,
        offset: u64,
        length: usize,
        priority: u8
    ) -> FFIResult<AsyncIOFuture> {
        // 创建操作ID
        let op_id = self.next_op_id.fetch_add(1, Ordering::Relaxed);
        
        // 创建任务
        let task = Arc::new(AsyncIOTask::new(op_id));
        
        // 存储任务
        if let Ok(mut tasks_guard) = self.tasks.write() {
            tasks_guard.insert(op_id, task.clone());
        }
        
        // 创建请求
        let request = AsyncIORequest::new(
            AsyncIOType::Read,
            file_path,
            Some(buffer),
            offset,
            length,
            None,
            None,
            op_id,
            priority
        );
        
        // 发送请求
        if let Some(sender) = &self.request_sender {
            sender.blocking_send(request)
                .map_err(|e| FFIError::IOError(format!("Failed to send request: {}", e)))?;
        } else {
            return Err(FFIError::InitializationFailed("Request sender not initialized".to_string()));
        }
        
        // 创建并返回未来对象
        Ok(AsyncIOFuture { task })
    }
    
    /// 异步写入文件
    pub fn async_write(
        &self,
        file_path: &str,
        buffer: Arc<Mutex<SafeMemoryBuffer>>,
        offset: u64,
        length: usize,
        priority: u8
    ) -> FFIResult<AsyncIOFuture> {
        // 创建操作ID
        let op_id = self.next_op_id.fetch_add(1, Ordering::Relaxed);
        
        // 创建任务
        let task = Arc::new(AsyncIOTask::new(op_id));
        
        // 存储任务
        if let Ok(mut tasks_guard) = self.tasks.write() {
            tasks_guard.insert(op_id, task.clone());
        }
        
        // 创建请求
        let request = AsyncIORequest::new(
            AsyncIOType::Write,
            file_path,
            Some(buffer),
            offset,
            length,
            None,
            None,
            op_id,
            priority
        );
        
        // 发送请求
        if let Some(sender) = &self.request_sender {
            sender.blocking_send(request)
                .map_err(|e| FFIError::IOError(format!("Failed to send request: {}", e)))?;
        } else {
            return Err(FFIError::InitializationFailed("Request sender not initialized".to_string()));
        }
        
        // 创建并返回未来对象
        Ok(AsyncIOFuture { task })
    }
    
    /// 异步寻求文件位置
    pub fn async_seek(
        &self,
        file_path: &str,
        position: SeekFrom,
        priority: u8
    ) -> FFIResult<AsyncIOFuture> {
        // 创建操作ID
        let op_id = self.next_op_id.fetch_add(1, Ordering::Relaxed);
        
        // 创建任务
        let task = Arc::new(AsyncIOTask::new(op_id));
        
        // 存储任务
        if let Ok(mut tasks_guard) = self.tasks.write() {
            tasks_guard.insert(op_id, task.clone());
        }
        
        // 创建请求
        let request = AsyncIORequest::new(
            AsyncIOType::Seek,
            file_path,
            None,
            0,
            0,
            Some(position),
            None,
            op_id,
            priority
        );
        
        // 发送请求
        if let Some(sender) = &self.request_sender {
            sender.blocking_send(request)
                .map_err(|e| FFIError::IOError(format!("Failed to send request: {}", e)))?;
        } else {
            return Err(FFIError::InitializationFailed("Request sender not initialized".to_string()));
        }
        
        // 创建并返回未来对象
        Ok(AsyncIOFuture { task })
    }
    
    /// 取消异步I/O操作
    pub fn cancel_operation(&self, op_id: u64) -> bool {
        if let Ok(mut tasks_guard) = self.tasks.write() {
            if let Some(task) = tasks_guard.get(&op_id) {
                task.set_state(AsyncIOTaskState::Cancelled);
                tasks_guard.remove(&op_id);
                return true;
            }
        }
        false
    }
    
    /// 获取当前运行中的任务数
    pub fn get_running_tasks_count(&self) -> usize {
        let available = self.semaphore.available_permits();
        self.max_concurrent_tasks as usize - available
    }
    
    /// 关闭调度器
    pub fn shutdown(&mut self) {
        // 关闭请求通道
        self.request_sender.take();
        
        // 清空任务映射
        if let Ok(mut tasks_guard) = self.tasks.write() {
            tasks_guard.clear();
        }
        
        // 关闭运行时
        if let Ok(mut runtime_guard) = self.runtime.lock() {
            if let Some(runtime) = runtime_guard.take() {
                runtime.shutdown_background();
            }
        }
        
        log::info!("Async I/O scheduler shutdown completed");
    }
}

/// 异步文件
pub struct AsyncFile {
    /// 文件路径
    path: String,
    /// 调度器引用
    scheduler: Arc<AsyncIOScheduler>,
    /// 当前文件位置
    position: AtomicU64,
}

impl AsyncFile {
    /// 打开文件
    pub fn open(path: &str, scheduler: Arc<AsyncIOScheduler>) -> FFIResult<Self> {
        // 检查文件是否存在
        let path_obj = Path::new(path);
        if !path_obj.exists() {
            return Err(FFIError::FileNotFound(format!("File not found: {}", path)));
        }
        
        Ok(AsyncFile {
            path: path.to_string(),
            scheduler,
            position: AtomicU64::new(0),
        })
    }
    
    /// 创建文件
    pub fn create(path: &str, scheduler: Arc<AsyncIOScheduler>) -> FFIResult<Self> {
        // 尝试创建文件
        File::create(path)
            .map_err(|e| FFIError::IOError(format!("Failed to create file: {}", e)))?;
        
        Ok(AsyncFile {
            path: path.to_string(),
            scheduler,
            position: AtomicU64::new(0),
        })
    }
    
    /// 异步读取数据
    pub async fn read(&self, buffer: Arc<Mutex<SafeMemoryBuffer>>, length: usize) -> FFIResult<usize> {
        let position = self.position.load(Ordering::Relaxed);
        
        let result = self.scheduler.async_read(
            &self.path,
            buffer,
            position,
            length,
            50 // 默认优先级
        )?.await;
        
        // 更新文件位置
        if let Ok(bytes_read) = &result {
            self.position.fetch_add(*bytes_read as u64, Ordering::Relaxed);
        }
        
        result
    }
    
    /// 异步写入数据
    pub async fn write(&self, buffer: Arc<Mutex<SafeMemoryBuffer>>, length: usize) -> FFIResult<usize> {
        let position = self.position.load(Ordering::Relaxed);
        
        let result = self.scheduler.async_write(
            &self.path,
            buffer,
            position,
            length,
            50 // 默认优先级
        )?.await;
        
        // 更新文件位置
        if let Ok(bytes_written) = &result {
            self.position.fetch_add(*bytes_written as u64, Ordering::Relaxed);
        }
        
        result
    }
    
    /// 异步寻求文件位置
    pub async fn seek(&self, position: SeekFrom) -> FFIResult<u64> {
        let result = self.scheduler.async_seek(
            &self.path,
            position,
            50 // 默认优先级
        )?.await;
        
        // 更新文件位置
        if let Ok(new_position) = &result {
            self.position.store(*new_position as u64, Ordering::Relaxed);
            Ok(*new_position as u64)
        } else {
            result.map(|_| 0)
        }
    }
    
    /// 获取文件路径
    pub fn path(&self) -> &str {
        &self.path
    }
    
    /// 获取当前文件位置
    pub fn position(&self) -> u64 {
        self.position.load(Ordering::Relaxed)
    }
}